Although the invention may be useful for connecting various structural components of aircraft or spacecraft, the present invention will be explained in the following in relation to a mechanical connection established between structural components of an aircraft fuselage structure, and in particular in relation to the mechanical connection of a frame to a stringer and/or to a skin of such a fuselage structure.
According to a conventional manner of forming an aircraft fuselage structure, a primary structure of the aircraft fuselage is formed with a skin stiffened by a plurality of frames and a plurality of stringers. The frames are used for stiffening the fuselage in a circumferential direction thereof, while the stringers are used for supporting the skin and stiffening the same in a longitudinal direction of the fuselage. The stringers may be connected directly to the skin and may be shaped as profiles of different cross-section, the cross-section having, for example, an L-shape, a T-shape or Ω-shape. In contrast, the frames may be shaped as Z-profiles or C-profiles.
In such a construction, it is desired to connect the frames to the skin either directly or via feet of the stringers acting as intermediate elements. This connection can be achieved, for example, according to the concept of the so-called differential frame, which means that the frame crosses above the stringer heads and is connected to the skin by means of additional, separate connecting elements, the so-called “clips”. Differential frames may be advantageous regarding the compensation of manufacturing tolerances of the individual workpieces during assembly.
In order to achieve a more lightweight aircraft fuselage structure, the fuselage skin, the frames and the stringers can be produced from a fiber-reinforced composite material, for example, from a synthetic material reinforced with carbon fibers. In this case, it is desirable, when the differential frame concept is chosen, to connect the frames to the skin by means of “clips” which are made from a composite material as well. Thereby, the weight of the fuselage may also be further reduced.
One example of an angled component for linking a fuselage skin to a ring frame of an aircraft is described in DE 10 2008 020 347 B4. This component is produced from a blank that has been cut out of a plane plate of a fiber-reinforced thermoplastic synthetic material. This blank is first heated in order to make the thermoplastic matrix of the fiber-reinforced synthetic material become soft. Then, the blank is deformed in one step along at least three folding lines in order to form an angled connecting component comprising an integrated stabilizing flange. The stabilizing flange is intended to enable the angled connecting component to support forces acting along the longitudinal direction of the aircraft fuselage, which is usually the direction parallel to the stringers. After the process of deforming the fiber-reinforced thermoplastic blank, the resulting workpiece, after cooling, is subjected to a cutting procedure to give the connecting component its desired final shape.
Although an angled connecting component as described in DE 10 2008 020 347 B4 may contribute to reducing the weight of an aircraft fuselage structure, the production of this conventional connecting component is complex, time-consuming and costly. This is due, in particular, to the need for different tools for deforming the blank after heating it, the tools being specially adapted to the shape of a particular connecting component or “clip”. Beyond this, the production of the conventional connecting components made of fiber-reinforced thermoplastic synthetic material requires a first cutting procedure in order to obtain the blank from the plate-shaped plane material, and then requires a further, complex three-dimensional cutting process for trimming the workpiece to its desired final dimensions and shape.
All this leads to a time-consuming production process, which is particularly undesirable because a great number of connecting components are needed within the structure of a complete aircraft.
As can be appreciated from the above, there is a need for a connecting element which may be produced rapidly and in great number at low effort and cost, while being reliable and lightweight and having sufficient strength, and for a method for producing such a connecting element.